1. Field of the Invention
The present invention relates generally to apparatus for processing a color video signal and more particularly to such apparatus which minimizes sideband interference and line-to-line level differences from a single tube-type color video camera having complementary color filters of the so-called checkered type.
2. Description of the Prior Art
In a black and white (monochromatic) video camera utilizing a charge-coupled device (CCD), a video signal of frequency fi is sampled at a sampling frequency fs. However, this results in a sideband component (known as aliasing noise) at the frequencies fs.+-.fi as shown in the frequency spectrum representation of FIG. 1. In a color video camera, however, the requisite color filter has different spectral sensitivities for achromatic color so that sideband components (or aliasing noise) are produced at the frequencies fs/2.+-.fi as shown in FIG. 2. Such fs/2.+-.fi sideband components are produced when the color filter is of the type having rows of color filter elements formed of two filter pixel units which alternate repeatedly in the horizontal direction.
This sideband component produced when an achromatic color scene is imaged, produces zero beat noise with the input frequency fi. Assuming a 510 H imager (that is, an imager having 510 filter pixels per line) with a sampling frequency fs=9.6 MHz, FIG. 3 represents that zero beat frequencies of 3.6 MHz, 3.2 MHz and 2.4 MHz are produced at the higher harmonics of the input frequency fi having fundamental frequencies 1.2 MHz, 1.6 MHz and 2.4 MHz, respectively. This zero beat noise gives rise to distortion in the picture produced from the video camera.
In order to remove the side band component in the color video signal produced when achromatic color is imaged, color video signaling processing has been proposed. While this apparatus operates satisfactorily for achromatic color signals, when that same apparatus is used with a chromatic color video signal, line-to-line level variations are induced in the luminance signal, resulting in interference in the picture displayed therefrom.